It is proposed to apply and expand the techniques and theory of redox systems to brain and to the in vivo control of the pterin- dependent hydroxylase reactions of biogenic amine synthesis. There are several subprojects (1) a critical examination of the application of redox techniques and theory worked out in liver to the more complicated situation in brain involving both metabolite measurements and subcellular enzyme distribution measurements of redox indicator enzymes, (2) isolation, purification and determination of the equilibrium constants under physiological conditions of dihydropterin reductase and dihydrofolate reductase by a spectrophotometric method (3) determination of subcellular distribution of the latter two enzymes in rat brain and comparison with the subcellular distribution of the hydroxylases, (4) determination in freeze-clamped liver and brain, by spectrophometric and fluorimetric assays, metabolites needed for redox calculations as well as the components of the pterin-hydroxylase systems--lactate, malate, alpha-glycerophosphate, pyruvate, oxaloacetate, alpha-ketoglutarare, dihydroxyacetone phosphate, isocitrate, the pterin cofactors, phenylalanine, tyrosine, dopamine, tryptophan and serotonin plus arterial and venous blood pO2 and pCO2 (5) estimation of the redox state of the pterin system and the mass-action ratios of the hydroxylase reactions in vivo both under normal conditions and under the conditions of altered flux through the pathway following electroconvulsive seizure.